I was a bit surprised to find my Apache httpd server had crapped out at 4am this morning. Looking in the last log I see
[Sun Mar 16 04:51:37 2008] [notice] SIGHUP received. Attempting to restart httpd: Syntax error on line 182 of /etc/httpd/conf/httpd.conf: Cannot load /etc/httpd/modules/mod_status.so into server: /etc/httpd/modules/mod_status.so: undefined symbol: ap_mod_status_reqtail

Thanks to the PC Notes blog of 黒さん I see this is a common problem (and I haven’t been hacked).

I updated by Apache httpd server yesterday, but didn’t bother to restart it. When Logrotate went to rotate the httpd logs at 4am it tried to tell httpd to do a reload (i.e. it sent a SIGHUP), but the running version of httpd wasn’t able to load the new version of httpd’s modules, so it crapped out.

A restart fixed everything.